1. Field of the Invention
The present invention relates to a method of forming an image using a photothermographic material. More particularly, the present invention relates to a method of forming an image using a photothermographic material that provides constant output images even in a thermal developing apparatus with high line speed at the time of thermal development.
2. Description of the Related Art
Recently, in the field of films for medical imaging and the field of films for graphic arts, there is a strong demand for reducing the volume of waste processing liquid from the viewpoint of environmental preservation and economy of space. There have been demands for technologies relating to use of a photothermographic material as a film for medical imaging and a film for graphic arts. In particular, there is a demand for a photothermographic material that is efficiently exposed by a laser image setter or a laser imager, and provides black-toned images with high resolution and sharpness. Such a photothermographic material can provide users with a more simple and ecological thermal developing system without the use of liquid processing chemicals.
Although there are similar demands in the field of general image forming materials, high image quality (i.e., excellent sharpness and fine graininess) is particularly required for images used in medical imaging where high image quality of excellent sharpness and granularity are necessary. Further, images with blue-black tones are preferred from the perspective of facilitating diagnosis. Various types of hard copy systems using pigment or dye, such as an inkjet printer and an electrophotograph system, are commonly used as a general image forming system. But none of these is satisfactory as an output system for medical images.
In general, thermal image forming systems using organic silver salts are described on page 279 to 291, Chapter 9, “Thermally Processed Silver Systems,” (Imaging Processes and Materials) Neblette, 8th edition, edited by D. Klosterboer, compiled by J. Sturge, V. Walworth and A. Shepp (1989), the disclosure of which is incorporated herein by reference.
A photothermographic material typically includes a photosensitive layer in which a photocatalyst (e.g., silver halide) of a catalytically active amount, a reducing agent, reducible silver salt (e.g., organic silver salt) and a toner for controlling the tone of a developed silver image as needed are dispersed in the matrix of a binder.
After an image is exposed thereon, a photothermographic material is heated to a high temperature (e.g., 80° C. or above) to cause an oxidation-reduction reaction between reducible silver salt (which acts as an oxidizing agent) and a reducing agent, thus providing a black silver image. The oxidation-reduction reaction is accelerated by the catalytic action of a latent image of the exposed silver halide (see U.S. Pat. (USP) No. 2,910,377 and Japanese Patent Application Publication (JP-B) No. 43-4924).
In view of the expanding fields of application and higher processing volume, it is necessary to record and develop images further rapidly. There has always been demand for improving processing capacity of the thermal developing process and thereby reducing processing time for the above-described photothermographic materials.
There has also been demand for improving adaptability of an image recording apparatus to the place where it is installed and to its environs. Thus the total size of the apparatus including an optical system for laser exposure and a thermal developing section needs to be reduced.
Another important problem in improving the developing process is to develop a photothermographic material adapted to high speed processing.
The problems facing thermal processing of photothermographic materals cannot be adequately addressed by handling the problems regarding the exposing and developing devices and the problems regarding the photothermographic material separately, as has often been the case in the past. Thus it is very difficult to achieve rapid developing process, to reduce the size of the image recording apparatus and to form constant images at the same time in the processing of photothermographic materals.